274 or THE EGG. 



terrestrial animals, and frequently several times a-year: most of 

 the lower aquatic animals, however, lay their eggs in the fall, 

 or during winter. In others, on the contrary, it occurs but 

 once during life, at the period of maturity, and the animal soon 

 afterwards dies. Thus the butterfly and most insects die 

 shortly after having laid their eggs. 



438. The period of ovulation is one of no less interest to 

 the zoologist than to the physiologist, since the peculiar cha- 

 racteristics of each species are then most clearly marked. 

 Ovulation is to animals what flowering is to plants ; and, in- 

 deed, few phenomena are more interesting to the student of 

 nature than those exhibited by animals at the pairing season. 

 Then their physiognomy is the most animated, their song the 

 most melodious, and their attire the most brilliant. Some 

 birds appear so different at this time, that zoologists are always 

 careful to indicate whether or not a bird is represented at the 

 breeding season. Fishes and many other animals are orna- 

 mented with much brighter colours at this period. 



439. Laying. After leaving the ovary, the eggs are either 

 discharged from the animal, that is, laid ; 

 or they continue their development within 

 the parent animal, as is the case in some 

 fishes and reptiles, as sharks and vipers, 

 which for that reason have been named 

 ova-viviparous animals. The eggs of the 

 mammalia are not only developed within 

 the mother, but become intimately united 

 to her ; this peculiar mode of development 

 has received the name of gestation. 



440. Eggs are sometimes laid one 

 by one, as in birds ; sometimes collec- 

 tively and in great numbers, as in frogs, fishes, and most 

 of the invertebrata. The queen ant of the African termites 

 lays 80,000 eggs in twenty-four hours; and the common 

 hair worm (Gordius) as many as 8,000,000 in less than one 

 day. In some instances they are united in clusters by a 

 gelatinous envelope; or are enclosed in cases or between 

 membranous discs, forming long strings, as in the eggs of the 

 Pyrula shell (fig. 285). The conditions under which the 

 eggs of different animals are placed, on being laid, are very 

 different. The eggs of birds, and of some insects, are deposited 



